I'm using Bottom of Sea by the way, but I don't think this will change the outcome in any ways.

Back tot he topic, whenever I try to go to my User CP, whether via upper bar or lower, it says

"vBulletin Message

Your submission could not be processed because a security token was missing.

If this occurred unexpectedly, please inform the administrator and describe the action you performed before you received this error."

Hm... I used to get the same error, though that was from me logging in, not from trying to get into the User CP. The reason it did it for me was because I had a different skin set as my default (The Bottom of the Sea one, actually). I think you need to change the skin back to the forum's current default (The Dark Illusionist one). Maybe you could try changing it back using the thing at the bottom of the page, then see if you can get into your User CP?

I checked I didn't get any errors here, must be something

I remember getting that when I joined. It'll almost certainly fix itself.

I changed my skin to Diamond Dialga and it seemed to have worked

Several of the skins were imported during a quasi-merger with the FreezeWarp was previous an administrator on, which had been running a significantly older version of vBulletin. I unfortunately do not have the means to support these skins, which seem to have problems with older browsers too.